{% macro form(action, submit) %}
<form action="{{action}}" method="POST">
    <div class="form-group">
        <input type="text" name="username" 
            placeholder="Username" class="form-control">
    </div>
    <div class="form-group">
        <input type="password" name="password" 
            placeholder="Password" class="form-control">
    </div>
    <div class="form-group">
        <input class="btn btn-primary" type="submit" 
               style="width: 6em;" value="{{submit}}">
    </div>
</form>
{% endmacro %}